UPDATE:
First off, i really think you should change the structure of your XML to something like: def.xml

<book>
<chapter id="1">
   <part id="1">
      <info>infoinfostuffhere</info>
      <def word="someword">some definition of the word</def>
      <extra>more info and notes</extra>
   </part>
   <part id="2">
      <info>infoinfostuffhere</info>
      <def word="someword">some definition of the word</def>
      <extra>more info and notes</extra>
   </part>
</chapter>
</book>
[download]

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Tr
+ansform">

<xsl:template match = "/book" >

   <xsl:for-each select = "chapter[@id]" >

      <h1> Chapter <xsl:value-of select="@id"/> </h1>
      <xsl:for-each select = "part[@id]" >
         <h3> Part <xsl:value-of select="@id"/> </h3>
         <i><xsl:value-of select="info"/></i><br/>
         <xsl:for-each select = "def[@word]" >
            <b><u><xsl:value-of select="@word"/></u></b>:<br/>
         </xsl:for-each>
         <xsl:value-of select="def"/><br/>
         <xsl:value-of select="extra"/><br/>
      </xsl:for-each>

   </xsl:for-each>

</xsl:template>

</xsl:stylesheet>
[download]

use strict;
use warnings;
use XML::LibXML;
use XML::LibXSLT;

my $xml  = XML::LibXML->new();
my $xslt = XML::LibXSLT->new();

my $source     = $xml->parse_file('def.xml');
my $style_doc  = $xml->parse_file('def.xsl');
my $stylesheet = $xslt->parse_stylesheet($style_doc);
my $results    = $stylesheet->transform($source);

print $stylesheet->output_string($results);
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jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)